Ca2+/calmodulin-dependent protein kinase II (CaMKII) is present abundantly in the central nervous system. CaMKII is deeply involved in the control of neuronal activity and the synaptic plasticity by serving as a protein kinase that phosphorylates various proteins and thereby modifies the functions of the proteins. Furthermore, CaMKII is considered to play an important role in higher brain functions including learning and memory, inhibition of epileptic seizure, and inhibition of brain disorder that may be caused by cerebral ischemia (see “PROTEIN, NUCLEIC ACID, AND ENZYME”, Vol. 47, No. 1: 51-57, 2002).
CaMKII present in the central nervous system has a multimeric structure whose component is an alpha subunit (CaMKIIα) and a beta subunit (CaMKIIβ). These subunits are highly homologous to each other. Each subunit has the protein kinase activity, the Ca2+/calmodulin-binding ability, and the capacity of association between subunits. The α subunit is expressed abundantly in the forebrain, while the β subunit is expressed abundantly in the cerebellum. It is therefore considered that the α subunit is mainly responsible for the above-mentioned CaMKII function.
Until now, simple knockout mice that have lost CaMKIIα protein itself have been produced. Behavior disorders having a relationship with memory and learning, and electrophysiological disorders have been found in these mice. Furthermore, the findings of vulnerability to both convulsion and cerebral ischemia have been also reported (see Science, Vol. 257: 201-206 and 206-211, 1992; Proc. Natl. Acad. Sci. USA, Vol. 92: 6852-6855, 1995; and J. Cereb. Blood Flow Metab., Vol. 16: 1-6, 1996). However, simple knockout mice have lost all of the following three functions: (1) a function as a protein kinase that phosphorylates proteins; (2) a function of binding to calmodulin that is a Ca2+-binding protein; and (3) a function of working as a structural protein through binding between CaMKII subunits or binding to other proteins. Thus, it was unclear which loss of function among these functions (1) to (3) was responsible for the various disorders found in the knockout mice. On the other hand, experiments using cultured neurons and brain slices suggest that the function (1) as a protein kinase is more important.
Hence, in order to elucidate the pathology of neuropsychiatric diseases and the molecular mechanisms of brain functions, it is necessary to produce and analyze a specific loss-of-functional animal in which the function (1) alone is specifically lost (so as to say, a “functionally knockout animal”), to distinguishably study the aforementioned functions (1) to (3) of CaMKII.